Three Seconds Longer
by Maks the Mushroom
Summary: Time, no matter the amount, has the power to alter lifetimes. So what if Hiro Hamada had managed to stall his brother for just a few seconds longer on that fateful day of the convention? How would that change his - and indeed, everyone else's - lives from that day onward? Big Hero 6 AU. Not spoiler free.
1. Okay

**A/N: Hello readers! So, this is my first Big Hero 6 fanfiction (actually my first fanfiction in a long time...go me). This "what if?" idea has been festering in my head ever since I saw the movie, and I just had to put it into writing. Anyways, hope you enjoy.**

**Disclaimer: I am not affiliated with Big Hero 6, Disney, or Marvel. These characters are not mine; I own nothing except this AU.**

* * *

><p>"<em>Someone has to help<em>."

Those four words rang painfully in Hiro's ears. _Of course_ Tadashi would say something like that. Tadashi, the golden boy, the selfless one, the one who would risk everything he had to save the people he loved. Always the protector, the savior, the hero-never anything less. Behind him, the flames broiled and lashed at the windows of the exhibition hall, flickering in his determined eyes. His brow was set, and his baseball cap cast a stony shadow across his face.

The scene around them had gone eerily quiet. Even the vicious roar of the flames dulled down to a whisper as Hiro stared pleadingly up at his brother.

And then, Tadashi was gone, racing up the steps towards the burning building.

But Hiro wasn't anything if he wasn't stubborn.

"_TADASHI!_" he all but screamed, lunging after his brother. His hand caught the back of Tadashi's blazer.

"What-" Tadashi whirled around, his eyes wide. "Hiro, I told you, let me-"

_**BOOM.**_

The two brothers flew backwards, crashing into the pavement. Tadashi's head cracked against the cold concrete, stars swimming in his vision as he tried to regain his bearings. "Hiro…" he mumbled. "Hiro!" His ears felt like they were filled with cotton, still ringing from the sound of the explosion. Sirens wailed in the distance, but all Tadashi cared about was the hazy sound of his brother's voice, still screaming out his name.

"Tadashi!"

"Hiro…"

Blazing embers rained down upon them, chunks of burning rubble and ash like snow. The exposition hall had begun to collapse.

"Tadashi!"

"Hiro!"

More people were coming now, paramedics and firemen frantically barking out orders. Weakly, Tadashi felt his hand brush up against a familiar hoodie-Hiro's hoodie.

"Hiro…" He carefully lifted up his head, suddenly aware of a wet feeling trickling down his neck.

His younger brother hurriedly crawled closer, one hand clutching Tadashi's signature baseball cap close to his chest. "C'mon," he coughed out. "We-We gotta go."

Tadashi nodded, dazedly trying to stumble to his feet. Almost immediately, though, his knees gave way, and he collapsed back down onto the pavement. Smoke burned through his lungs, the ash stinging his eyes. Quickly, Hiro slung his arm beneath his brother's chest, hauling him to his feet.

"You-You alright?" Tadashi asked, wrapping his arm around Hiro's shoulders in order to keep himself steady.

Despite himself, Hiro let out a short laugh. "You're really the one asking me that?"

Tadashi chuckled weakly in response. "I have to, I'm your older broth-" He broke off in a violent fit of coughs, and Hiro quickly moved to steady him.

Paramedics soon swarmed around them, quickly taking Tadashi and helping him into an ambulance. Hiro watched his brother go nervously, barely paying attention to the paramedics fussing around him. Blood had soaked through the elbow of his sweatshirt, but he hardly registered the pain. All he could think about was Tadashi.

Tadashi was going to be okay.

He had to be.

* * *

><p>If there was one thing Hiro hated, it was hospitals. The sterile smell stung his nostrils, even more so now with the ash and smoke still infesting his lungs. An unbearable silence pressed in on him from all sides. It was far too tense, too nervous waiting in the lobby; if nothing happened anytime soon, Hiro swore he would scream. The pristine white walls, the shining tiles, the harsh light of the parking lot's street lamps flooding through the windows all seemed to mock his pain as he waited anxiously for news on his brother.<p>

"Hiro, please stop pacing," said Honey Lemon gently from her seat. "You need to rest-"

"I can't!" he snapped, much more harshly than he intended. Nervously, he tugged a hand through his already messy black hair, letting his eyes slip closed for a moment. "What if Tadashi's not okay, o-or he's hurt really badly, or…"

"Dude, chill," Gogo remarked, her legs draped across the cold metal arm of the lobby chair. "You saw Tadashi get into the back of the ambulance, right? He'll be _fine_."

Hiro swallowed back the lump in his throat. Tadashi had taken the brunt of the explosion when it hit; while Hiro only had a scraped elbow and a couple of bruises to show for it, his brother had at the very least a head wound. Hiro may not have been well versed in medical science, but from the way his brother was stumbling around after the explosion, he figured it couldn't have been good.

A doctor called for the Hamada family, and Aunt Cass quickly sprang up and hurried over, her hands clutched to her chest in fear. With a sigh, Hiro sank down into the vacant seat, slumping wearily against the hard plastic. How long had they been here? Three hours now? Four? Wasabi had already left, insisting that he had to adhere to his precise sleeping schedule but giving the Hamadas his condolences anyways, and Fred was snoring comfortably in the corner, sprawled out across three different chairs. Both Honey and Gogo were still relatively alert though, with Honey doing her best to comfort both Aunt Cass and Hiro. Gogo just simply refused to leave.

"Hey," she said, gently nudging Hiro's arm. "It's be okay. Tadashi's a strong man. He'll pull through."

Hiro frowned, fiddling absently with the zipper of his jacket. "Yeah, but-"

"Hiro."

Hiro's head shot up at the sound of Aunt Cass' voice. "The doctors said we can go visit Tadashi now," she told him.

Quick as a flash, Hiro leapt out of his seat and scrambled over, scrawny limbs flailing as he rushed to Aunt Cass' side. "Where is he? Is he okay? What happened to him?" Questions tumbled frantically out of the young boy's mouth, his brown eyes wide.

Aunt Cass chuckled softly. "Whoa, hey, slow down kiddo," she smiled. "Tadashi's fine. He had a concussion and a bad cut on the back of his head, but the doctors were able to stitch him up, and he'll be as good as new in no time."

Relief washed over Hiro's face. "Oh thank _God_." Quickly, he turned around and gestured to the rest of the group. "C'mon!"

Hiro and Aunt Cass hurried through the winding hallways, closely followed by Honey, Gogo and (a still rather groggy) Fred. Eventually, they came to a stop in front of a room labeled '614'.

"Tadashi?" Hiro called out tentatively, pushing the door open a crack.

His brother lay propped up in the hospital bed, casually flipping through a magazine one of the nurses had given him. A thick bandage was wrapped around his head, but other than that, he looked perfectly fine. Just normal, calm, collected Tadashi-even his hair still seemed perfectly combed. Unbelievable.

Tadashi glanced up at the sound of his brother's voice. "Took you long enough, bonehead," he joked, setting down the magazine.

"Hey, you're the one calling me bonehead?" Hiro replied, one eyebrow raised as he walked closer. "You're the one who tried to run into a burning building."

Tadashi pursed his lips in mock thought. "True, true."

Hiro stood at his brother's bedside for a moment, rocking back and forth on the balls of his feet, before pulling him into a tight hug. "I'm so glad you're okay," he mumbled.

Tadashi smiled, gently returning his embrace. "Me too." His eyes flickered over the rest of the group standing there, and a worried frown slowly formed on his face. "Hey, is everyone else alright?" he asked. "What happened? Did they find Professor Callaghan?"

Honey and Gogo shared a look. "Tadashi…" Honey began, hands fumbling with the strap of her purse. "The firefighters looked everywhere, they really did, but…"

"They couldn't find his body," Gogo interjected. " Professor Callaghan's dead."

Tadashi's heart dropped like a stone.

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><p><strong>AN: So, there you have it. I apologize now if I didn't get the characterization quite right; I'm still struggling to get a full grasp of these characters. Hope you enjoyed, please review if you can! **


	2. Tired

**A/N: I SWEAR I AM ALIVE!**

**I sincerely apologize for the two weeks it took to write this next chapter. With the end of the semester coming up, my teachers have been loading me with several different projects, and unfortunately, real life takes precedence over writing.**

**Anyways, I'll try to update this story every week, but we'll see if I can actually stick to that goal. I'm quoting the movie here, but: "Sometimes life doesn't go the way you plan."**

**Hope you enjoy this next chapter. Tadashi's mindset is very interesting to explore.**

**Disclaimer: I don't own Big Hero 6. Although I would like a Baymax for Christmas.**

~o*o~

Tadashi was released from the hospital two days later.

Hiro had remained stubbornly by his side for the entire duration of his stay, poking and prodding his brother about trivial things such as the college cafeteria and the latest episode of their favorite TV show, if only to get the older boy talking and smiling again. But despite all of Hiro's valiant efforts, Tadashi remained listlessly silent. The man had hit a rut. No matter how hard he tried, he could hardly manage half a grin or a dull two-word response to any of Hiro's questions. His eyes scanned unseeingly over the pages of some book the nurses had given him to pass the time - he didn't even know what it was titled, to be honest - while images of flames and smoke danced in his vision.

He let Professor Callaghan die. He failed to save him.

On the drive home, Tadashi stared silently out the window of his aunt's truck, Hiro's attempts to make conversation with him again bouncing uselessly off of him like tennis balls against a brick wall. How could his brother still look at him, even after he had failed to save one of his heros? How could anyone, really? He had made it his purpose in life to help people, and he had failed.

When someone needed him most, he failed.

The truck grew uncomfortably silent as they drove past the school. The destroyed exposition hall had been mostly cleaned up by now, leaving a black scar on the once-bright campus. Distantly, Tadashi could see tiny pinpricks of candlelight dancing on the charred steps.

"Stop the car."

Aunt Cass shot him a worried glance. "Tadashi..."

"Stop the car."

With a soft sigh, Aunt Cass pulled over to the side of the road. Tadashi wordlessly stepped out of the truck, wringing his baseball cap in his hands. "There's - There's something I need to do," he said. "I'll be right back."

Aunt Cass nodded, one hand on Hiro's shoulder to prevent him from going after his brother. "We'll be here when you're done, sweetie."

A large lump swelled in Tadashi's throat, but he quickly swallowed it back and shakily began walking towards the memorial. In his opinion, it didn't do the roboticist justice. Professor Callaghan had done so much, meant so much; he deserved more than just a tiny framed picture and some flowers and candles. Tadashi dimly remembered someone mentioning something about a memorial service being held the following week, but it had gotten lost in his mind, disappearing into the haze of guilt and grief that filled his thoughts like smoke.

Slowly, Tadashi sank to his knees in front of the memorial, tears already welling in his eyes. Professor Callaghan's picture smiled serenely back at him.

"I'm so sorry," he mumbled, his baseball cap clutched tightly in one hand. "I'm so sorry."

It felt like he was nine again, staring at his parents' graves. Once again, his role model, his guardian, his mentor had died, and it was all his fault.

"I could've gone in there. I should've gone in there. I should've _saved you_!"

It was all his fault.

"I'm so sorry…"

~o*o~

Aunt Cass gently rapped on the screen door closing off Tadashi's half (or fourth, really) of the attic. "Tadashi, sweetie?" she called out.

A faint grunt sounded in response.

"I did some of your laundry," she continued, adjusting one of the folded shirts in the basket she carried. "I know you usually like to do your own, but I figured, you know, since I was doing some of Hiro's laundry, I'd just…"

The screen moved back, revealing a bleary-eyed Tadashi leaning against the wall. His normally well-kept hair was in complete disarray, and a bit of stubble was growing along his jaw. "Thanks, Aunt Cass," he mumbled, shooting her a dull smile as he took the basket from her. "I'll be sure to put it away."

Aunt Cass watched her nephew with a frown, wrapping her arms tightly around herself. "Well, if you need anything else…"

"All finished Aunt Cass!" Hiro bounded into the room, the familiar gap-toothed grin on his face. "The cafe's all closed up."

Aunt Cass beamed, pulling Hiro into a quick hug. "That's my boy," she grinned. "Oh, and I put some laundry on your bed. You know, you really should learn to empty out your jacket pockets."

Hiro frowned. "What're you-"

Aunt Cass pushed a tiny object into his hand. "My...microbot?" Quickly, Hiro crossed over to his desk and put the little robot into a petri dish on his shelf. "Th-Thanks, I'll...take a look at it later."

His aunt bounced a little in excitement. "Well, I'll let you get some rest now," she said, all but skipping out of the room. "Got a big first day of college tomorrow!"

Hiro couldn't help but roll his eyes at his aunt's antics. "G'night." He couldn't really blame her though; after all, it's not every day you start school at one of the most prestigious colleges in the city.

Happily, Hiro turned to look at the other side of the room. "Hey, Tadashi-"

But the light was off, and the screen door was shut again.

~o*o~

Tadashi wearily dragged himself out of bed the next day. He didn't want to go back to the college. Every building, hallway, classroom - everything - reminded him of Professor Callaghan...and moreover, his failure to save him. But Tadashi had a duty to his little brother, so he haphazardly plopped his baseball cap onto his head, plastered a smile on his face, and ushered Hiro out the door of the cafe.

He tried his best not to let his lack of enthusiasm show as he stepped into his first class, which he coincidentally shared with Hiro and Gogo. The young woman noisily popped her bubblegum and motioned the pair over, the tiniest smile flickering across her face when she saw Hiro's nervousness immediately dissipate. Tadashi waved him off, opting for a seat in the back of the room.

He was just...tired.

Tired of being reminded of his mentor. Tired of hearing the phrase, "He's still with us, as long as we remember him." Tired of the sympathetic looks and pats on the back from his friends.

Just...tired.

He fidgeted uncomfortably in his seat as a moment of silence was called over the intercom. The rest of the day passed by in an uneventful blur, with Tadashi hardly paying any attention even in his favorite classes. Gogo ended up taking over showing Hiro around the school and helping set up his personal lab space; Tadashi clearly didn't feel up to it.

With a soft groan, Tadashi stumbled into his personal lab, slumping into the rolling chair in the corner. He could still remember it - the day he showed his little brother Baymax for the first time, and Professor Callaghan just so happened to walk in and cement Hiro's decision to apply. If only he hadn't been so insistent on getting his brother to go here, maybe then Professor Callaghan would still be alive…

Tadashi shook his head, reaching into a drawer and pulling out the file of notes on Baymax's design. Professor Callaghan's familiar cursive decorated several of the blueprints, and Tadashi suddenly remembered those many early mornings he spent in the professor's office, discussing the nursebot's skeletal structure and initial programming. A large lump swelled in his throat again, and he quickly swallowed it back and hastily continued rifling through the papers.

"Ow!"

Tadashi clutched at his finger, pressing the bleeding papercut to his lips in an effort to stem the pain. The familiar sound of a balloon inflating filled the room.

"Hello, I am Baymax, your personal healthcare companion. I was alerted to your need for medical attention when you said, 'Ow'."

Tadashi smiled thinly at the robot. "Hey, buddy."

The robot blinked once at him before looking down at the diagram appearing on his belly. "On a scale from one to ten, how would you rate your pain?" he intoned.

"A one," Tadashi answered easily. "I'm fine, Baymax, really."

"I will scan you now." A faint whirring noise came from the robot's cameras. "Scan complete. You have a minor epidermal cut on your right forefinger. I suggest an antibiotic ointment and a bandage."

Tadashi couldn't help but chuckle as Baymax gently applied some ointment to his finger before dispensing a bandage for him. "Thanks," he said. "I'm satisfi-"

"Additionally," Baymax continued, "your neurotransmitter levels are strangely low. I would recommend a high carbohydrate meal with a banana, and some exercise or a nap."

Tadashi blinked in confusion at the robot. "I - I'm fine, Baymax," he finally managed to say. "Really, I'm-"

"It is not wise to ignore conditions like this, Tadashi," Baymax intoned. "This could be damaging to your health."

Tadashi laughed sheepishly, running a hand over his face. "Wow, Professor Callaghan was right about your programming…" His eyes flicked over to the heap of notes on his desk. He never did get the chance to show the professor the robot, but he was sure the professor would find some way to improve the design.

"Nothing is ever really finished, Mr. Hamada," he had said, and Tadashi could've sworn for a moment a dark shadow passed over his eyes. "There's always room for more testing, more improvement."

With a sigh, Tadashi stood up from his chair, tilting his head to the side thoughtfully as he studied Baymax's figure. A thousand different ideas began to pop into his head, and he found his fingers itching to pick up a pencil.

"I'm gonna make you proud, Professor. I promise."

~o*o~

**A/N: Like I said, Tadashi's mindset after the fire is very interesting to explore. I had some difficulty grappling with it at first, considering he's usually such a bright spirit in the movie, but I think I did alright. Hope you enjoyed! Please review if you can!**


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